There exists today a growing need to expand the use of traditionally office-based computer applications (e.g., word processing programs, electronic mail, etc.) to remote locations such as the home or car. Data files and/or messages generated by such applications, residing on hosts having local-area network/wide-area network (LAN/WAN) connectivity, are typically transmitted from one location to another using high-speed protocols such as the so-called Transport Control Protocol/Internet Protocol (TCP/IP). In order to extend the use of these applications to remote locations not serviced by a LAN/WAN, it is necessary to establish connections between LAN/WANs and other non-similar communication networks, such as wireless communication systems.
A major difficulty in connecting LAN/WANs to wireless communication systems is the large disparity in their available transmission bandwidths and hence, their throughput capacities. It is not atypical for a wireless communication system to have a transmission bandwidth 10 times less that of a LAN/WAN. This disparity also contributes to the widely differing protocols used in LAN/WANs and wireless communication systems. The lower throughput capacities associated with wireless communication systems has led to the use of circuit-switched techniques, whereas the higher throughput capacities associated with LAN/WANs has led to the use of packet-switched techniques.
FIG. 1 illustrates an example of a typical, prior art circuit-switched communication (100). When initial source data (101) becomes available, a channel set-up period (107) is required to establish a communication path between the source and the destination. For example, in the wireless case, the channel set-up period (107) may be the time required to request and obtain usage of a particular radio frequency (RF) carrier. Regardless of the channel type, the channel, once established, remains dedicated for the exclusive use of the source and destination.
Having established the channel, the initial source data is transmitted (109) to the destination. As additional source data (103, 105) becomes available, it is immediately transmitted (113, 117) through the channel. When necessary, usage of the channel is then discontinued during a channel tear-down period (119). Advantages of circuit-switched techniques are the low overhead requirement (i.e., the amount of throughput capacity required for the transmission of information other than the source data), as well as the low delay (i.e., the time difference between the availability of source data and its actual transmission). The periods of channel inactivity (111, 115) in between periods of data availability, however, are a disadvantage of circuit-switched techniques. This is a direct result of the dedicated use of the channel; other sources are unable to utilize the channel. These advantages and disadvantages make the use of circuit-switched techniques most efficient for longer communications, such as file transfers or fax transmissions.
FIG. 2 illustrates an example of a typical, prior art packet-switched communication (200). A key difference between packet-switched and circuit-switched methods is that the channel, when used in a packet-switched manner, is not dedicated and is available for use by multiple sources and destinations. Once available, the initial source data (101) is partitioned into data packets (203, 207, 211) for transmission. The data packets (203, 207, 211) occupy available time-slots that include capacity for overhead data (201, 205, 209). Due to the commonality of the channel, the overhead data (201, 205, 209) typically comprises target destination identification information so that data intended for a particular destination may be properly routed.
As additional source data (103, 105) becomes available, it is again formatted into data packets (217, 221, 227) and placed into available time-slots with their associated overhead data (215, 219, 225). Advantages of packet-switched methods are that set-up/tear-down periods are not required. Also, multiple communications may be intermingled on the channel. Assuming the use of channels having equivalent bandwidths, packet-switched methods are less efficient relative to circuit-switched methods due to the additional overhead, typically leading to larger throughput delays. Delays are further lengthened when time-slot availability is reduced due to heavy use of the channel. These disadvantages can be overcome by increasing the packet-switched channel's transmission bandwidth, if possible, to accommodate the larger overhead and need for additional time-slots. Typically, packet-switched techniques are most efficient in the transmission of shorter communications, such as electronic mail messages or paging services.
In order to establish connectivity between LAN/WANs and wireless communication systems, the incompatibilities of their respective packet-switched and circuit-switched protocols need to be resolved. One solution to this problem is to directly transmit the packet-switched data, including the overhead data for each packet, over a circuit-switched (i.e., wireless) channel. This is inadequate, however, because the differences in throughput capacities would require an inordinate amount of packet-switched information to be buffered prior to transmission over the circuit-switched channel. Even if the circuit-switched channel has sufficient bandwidth, this solution becomes inefficient due to channel inactivity during periods of low packet volumes.
Another solution is to establish a circuit-switched transmission for each data packet or group of data packets. While this solution might be acceptable for low volumes of packets, it becomes severely inefficient for increasing packet volumes due to the set-up and tear-down overhead Therefore, a need exists for a method of transmitting packet-switched data in an efficient manner over circuit-switched (particularly wireless) communication channels.